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(by their attachment to the extensor tendons) as extensors of the fingers, acting on both interphalangeal joints.
M. Flexor Pollicis Longus.-The flexor pollicis longus arises, beneath the flexor digitorum sublimis, by fleshy fibres, from the volar surface of the body of the radius in its middle twofourths, and from a corresponding portion of the interosseous membrane. It has an additional origin, occasionally, from the medial border of the coronoid process of the ulna (Fig. 348, p. 389). Its radial origin is limited proximally by the oblique proximal part of the volar margin of the radius and the origin of the flexor digitorum sublimis, and distally by the insertion of the pronator quadratus muscle.
The muscle ends, proximal to the wrist, in a tendon, which passes over the pronator quadratus into the hand beneath the transverse carpal ligament, and is enveloped in a special mucous sheath.
In the palm the tendon is directed distally along the medial side of the thenar eminence, between the flexor brevis and adductor muscles of the thumb, to be inserted into the base of the terminal phalanx of the thumb on its volar surface.
SUPERFICIAL FLEXOR ORIGIN
M. Pronator Quadratus.-The pronator quadratus is a quadrilateral fleshy muscle, occupying the distal fourth of the forearm. It is placed beneath the deep flexor tendons, and arises from the distal fourth of the volar margin and surface of the ulna (Fig. 348, p. 389).
It is directed transversely laterally to be inserted into the distal fourth of the volar surface of the radius, and into the narrow triangular area on its medial side, in front of the attachment of the interosseous membrane (Fig. 348, p. 389).
The pronator quadratus is subject to considerable variations. It may even be absent; or it may have an origin from radius or ulna, or from both bones, and an Insertion into the carpus.
The muscle is placed deeply in the forearm, being concealed by the superficial layer of muscles and by the flexor digitorum sublimis.
FIG. 349.-THE DEEPEST MUSCLES ON THE VOLAR ASPECT
Nerve-Supply.-Volar interosseous branch of the median (C. 7. 8. T. 1.).
Actions. The muscle is a flexor of the wrist and thumb, acting in the latter movement on the metacarpal bone and both phalanges.
The muscle is placed deeply in the distal part of the forearm, and is wholly concealed by the tendons of the muscles which descend, under cover of the transverse carpal ligament, to the wrist and fingers. The radial artery and its accompanying veins pass over it at its insertion into the radius.
=ADDUCTOR POLLICIS (transverse head)
OPPONENS POLLICIS FLEXOR POLLICIS BREVIS (superficial part) ADDUCTOR POLLICIS (oblique head)
FLEXOR DIGITORUM SUBLIMIS TENDON
DIGITAL SHEATH FLEXOR DIGITORUM PROFUNDUS
FLEXOR DIGITORUM PROFUNDUS
ABDUCTOR DIGITI QUINTI (cut)
THIRD VOLAR INTEROSSEOUS MUSCLE
FLEXOR DIGITI QUINTI
TENDONS OF THIRD AND
FIG. 350.-THE PALMAR MUSCLES (Right Side).
Nerve-Supply.-Volar interosseous branch of the median nerve (C. 7. 8. T. 1.). Action. The muscle acts along with the pronator teres in producing pronation of the forearm.
SHORT MUSCLES OF THE HAND.
The short muscles belonging to the hand, in addition to the palmaris brevis and the lumbrical muscles, already described, include the six muscles of the
thumb which produce the thenar eminence, the three muscles of the little finger, which form the hypothenar eminence, and the interossei muscles, which are deeply placed between the metacarpal bones.
Muscles of the Thumb.
The short muscles of the thumb are the abductor, opponens, and flexor brevis (with its deep portion, interosseus primus volaris), and the adductor muscle, subdivided into two heads-oblique and transverse.
M. Abductor Pollicis Brevis.-The abductor pollicis brevis (O.T. abductor pollicis) arises by fleshy fibres from the tubercle of the navicular, the ridge of the greater multangular, the volar surface of the transverse carpal ligament, and from
Lesser multangular bone-
Flexor carpi radialis
First dorsal interosseous muscle
First volar interosseous muscle
Abductor digiti quinti (origin)
Flexor carpi ulnaris (insertion)
Flexor carpi ulnaris (insertion)
Third volar inter-
Fourth dorsal interosseous
Second dorsal interosseous
Third dorsal interosseous
FIG. 351.-MUSCLE-ATTACHMENTS TO THE VOLAR ASPECT OF THE CARPUS AND METACARPUS.
tendinous slips derived from the insertions of the palmaris longus and abductor pollicis longus muscles (Fig. 350, p. 391). Strap-like in form, and superficial in position, it is inserted by a short tendon into the radial side of the first phalanx of the thumb at its proximal end, and into the capsule of the metacarpo-phalangeal joint.
Nerve-Supply. Median nerve (C. 6. 7.).
Actions. The muscle acts on the thumb at both the carpo-metacarpal and metacarpophalangeal joints. It abducts and draws forward the thumb.
M. Opponens Pollicis.-The opponens pollicis arises by fleshy and tendinous. fibres from the volar surface of the transverse carpal ligament and from the ridge. on the greater multangular bone. It is partially concealed by the preceding muscle.
Extending distally and laterally it is inserted into the whole length of the lateral border and the radial half of the volar surface of the first metacarpal bone (Fig. 351, p. 392).
Nerve-Supply.-Median nerve (C. 6. 7.).
Action. It acts solely on the first metacarpal bone, in the movement of opposition of the thumb.
M. Flexor Pollicis Brevis.-The flexor pollicis brevis consists of two parts. a. The superficial part of the muscle, partly concealed by the abductor pollicis brevis, arises, by fleshy and tendinous fibres, from the distal border of the transverse carpal ligament, and sometimes from the ridge of the greater multangular.
It is inserted into the radial side of the base of the first phalanx of the thumb, a sesamoid bone being present in the tendon of insertion.
b. The deep part of the muscle (interosseus primus volaris) arises from the medial side of the base of the first metacarpal bone.
It is inserted into the medial side of the base of the first phalanx of the thumb along with the adductor pollicis.
This little muscle is deeply situated in the first interosseous space, in the interval between the adductor pollicis obliquus and the first dorsal interosseous muscle. It may be regarded as homologous with the volar interossei muscles, with which it is in series.
Nerve-Supply. Median nerve (C. 6. 7.).
Actions. It is a flexor of the thumb and assists also in the movement of opposition of the thumb to the fingers.
M. Adductor Pollicis.-The adductor pollicis is separated into two parts by the radial artery.
(1) The oblique head lies deeply in the palm, covered by the tendons of the long flexors of the thumb and fingers. It arises by fleshy fibres from the volar surfaces. of the greater and lesser multangular and capitate bones, from the sheath of the tendon of the flexor carpi radialis, from the volar surfaces of the bases of the second, third, and fourth metacarpal bones, and from the volar ligaments connecting these bones together (Fig. 351, p. 392).
It is inserted by a tendon, in which a sesamoid bone is developed, into the medial side of the base of the first phalanx of the thumb. At its lateral border a slender slip separates from the rest of the muscle, and passing obliquely, deep to the tendon of the flexor pollicis longus, is inserted into the lateral side of the base of the first phalanx along with the superficial part of the flexor pollicis brevis.
(2) The transverse head, lying deeply in the palm beneath the flexor tendons, arises by fleshy fibres from the medial ridge on the volar aspect of the body of the third metacarpal bone, in its distal two-thirds (Fig. 351, p. 392), and from the fascia covering the interosseous muscles in the second and third spaces.
Triangular in form, it is directed laterally, over the interossei muscles of the first two spaces, to be inserted by tendon into the medial side of the base of the first phalanx of the thumb along with the oblique head.
Nerve-Supply. Deep branch of the ulnar nerve (C. 8. (T. 1.)).
Muscles of the Little Finger.
The short muscles of the little finger are the adductor, opponens, and flexor brevis digiti quinti.
M. Abductor Digiti Quinti.—The abductor digiti quinti is most superficial. It arises from the pisiform bone and from the tendon of the flexor carpi ulnaris and its ligamentous continuations (Fig. 351, p. 392).
It is inserted by tendon into the medial side of the base of the first phalanx of the little finger.
Nerve-Supply.-Deep branch of the ulnar nerve (C. 8. (T. 1.)).
Actions. The muscle separates the little finger from the ring finger, and assists in flexion of the finger at the metacarpo-phalangeal joint.
M. Opponens Digiti Quinti.-The opponens digiti quinti arises under cover
bones on their volar surfaces (Fig. 351, p. 392). The chief tendon is that to the second metacarpal bone.
The muscle is superficial except near its insertion. Its tendon, in the distal half of the forearm, is an important guide to the radial vessels, which are placed to its radial side. After passing beneath the transverse carpal ligament the tendon is concealed by the origins of the short muscles of the thumb, and is crossed, from medial to lateral side, by the tendon of the flexor pollicis longus. Besides the mucous sheath enveloping the tendon beneath the ligament, a mucous bursa is placed beneath the insertion of the tendon.
Nerve-Supply.-Median nerve (C. 6.).
Actions. This muscle has a threefold action. It is mainly a flexor of the elbow and wrist, but it also acts as an accessory pronator of the forearm.
M. Palmaris Longus. The palmaris longus arises also from the common flexor tendon from the medial epicondyle of the humerus, from the fascia over it, and from intermuscular septa on each side.
M A1 2 3 B 4 5 CD 6
It forms a short fusiform muscle, which ends, in the middle of the forearm, in a 7 long flat tendon. This pierces
the deep fascia, near the wrist, E and passing over the transF verse carpal ligament, is in
serted (1) into the surface of the transverse carpal ligament, and (2) into the apex of the thick central portion of the palmar aponeurosis. A tendinous slip is frequently sent to the short muscles of the thumb and the fascia covering
J I 98 H G
FIG. 344.-DISTAL SURFACE OF A SECTION ACROSS THE RIGHT them.
DIGITORUM SUBLIMIS; D, PALMARIS LONGUS; E, FLEXOR CARPI ULNARIS;
The palmaris longus is the Smallest muscle of the forearm. In the distal third of the H, EXTENSOR POLLICIS LONGUS; I, EXTENSOR DIGITORUM COMMUNIS AND forearm its tendon is placed EXTENSOR DIGITI QUINTI PROPRIUS; J, ABDUCTOR POLLICIS LONGUS; K, directly over the median
EXTENSOR CARPI RADIALIS BREVIS; L., EXTENSOR CARPI RADIALIS LONGUS;
nerve, along the radial border
M, BRACHIORADIALIS. a, Radius; b, Interosseous membrane; c, Ulna.
1, Superficial ramus of radial nerve; 2, Radial artery; 3, Volar inter- of the tendons of the flexor osseous artery; 4, Volar interosseous nerve (underneath flexor pollicis
longus); 5, Median nerve; 6, Ulnar artery; 7, Ulnar nerve; 8, Dorsal
interosseous artery; 9, Dorsal interosseous nerve.
The palmaris longus is the
most variable muscle in the body, and is often absent (10 per cent).
Nerve-Supply.-Median nerve (C. 6.).
Actions. The muscle assists in flexion of the elbow and wrist. It also by tightening the palmar aponeurosis deepens the hollow of the hand and helps to flex the fingers.
M. Flexor Carpi Ulnaris.-The flexor carpi ulnaris muscle has a double origin, from the humerus and from the ulna. (1) It arises from the common tendon attached to the medial epicondyle of the humerus, from the fascia over it, and from a lateral intermuscular septum. (2) By means of the deep fascia of the forearm it obtains an attachment to the medial border of the olecranon and the dorsal margin of the ulna in its proximal three-fifths.
The fleshy fibres join a tendon which lies on the anterior border of the muscle and is inserted into the pisiform bone, and in the form of two ligamentous bands (piso-hamate and piso-metacarpal) into the hamulus of the os hamatum, and the proximal end of the fifth metacarpal bone (Fig. 351, p. 392).
The muscle is superficially placed along the medial border of the forearm. It conceals the flexor digitorum profundus muscle, the ulnar nerve (which enters